A combination of electron microscopic, histochemical and electrophysiological methods were utilized to investigate the synaptic organization of the ninth and tenth paravertebral sympathetic ganglia of the bullfrog. The neurons were unipolar and were innervated by a single preganglionic axon. The cholinergic preganglionic fiber stained for acetylcholinesterase and was observed in both the light and electron microscope to spiral around the axon hillock of the ganglion cell before arborizing and making synaptic contact with the neuron. Most synapses were located on the soma near the axon hillock region, with electron microscopic features typical for cholinergic junctions. The axosomatic location of the synapses was manifested physiologically by a decrease in membrane resistance (increased conductance) at the peak of the fast EPSP and by a demonstrable reversal potential for the fast EPSP. BIBLIOGRAPHIC REFERENCE: Weitsen, H.A. and Weight, F.F.: Synaptic innervation of sympathetic ganglion cells in the bullfrog. Brain Res. 128: 197-211, 1977.